Electrically heated appliance with expansion stabilizer



J '25 1 1 J; N. POLNKA 2,797,292

ELECTRICALLY HEATED APPLIANCE WITH EXPANSION STABILIZER Filed June 29, 1954 yllm Jul/N 7V pal/M141 BY K ATTORNEY ELECTRICALLY HEATED APRLIANCE WETH EXPANSION STABHLIZER John N. Polivka, Minneapolis, Minn.,, assignor to General Mills, Inc, a corporation of Delaware Application June 29, 1954, Serial No. 446,659

12 Claims. (Cl. 219-25) This invention relates in general to electrically heated appliances and pertains more particularly to a temperature control means that will find appreciable utility in electric flatirons.

One problem that has long plagued the appliance industry, especially in the electrically heated fiatiron art, has been a temperature control arrangement that will, within practical limits, reflect in its operation the average temperature of the soleplate and which will at the same time be low in cost. In the past these two desiderata have been at odds with each other and therefore either a fairly accurate temperature control feature has been incorporated into the appliance or such sensitivity of control has been sacrificed in favor of lower manufacturing cost.

Accordingly, one object of the invention is to provide a thermostatic control that will be accurate, that is one well within the desired practical limits of temperature control, and which can be fabricated from low cost materials at little expense. More specifically, it is an aim of the invention to utilize the soleplate, if the invention is utilized in conjunction with an electric fiatiron, as one expansion member and to employ as the other expansion member a member having a low coeficient of expansion as well as a low rate of heat transfer. In this way the second mentioned member will have little tendency to expand and, due to its low rate of heat transfer, may be anchored directly at one end thereof to the soleplate without objectionable heat transfer thereto from the soleplate.

Another object is to provide a temperature control for electrically heated appliances that can be readily installed at the factory and which will function satisfactorily over long periods of time without attention on the part of the user.

A further object of the invention is to provide a thermostat especially suited for use in an electric iron, at portion of which is flexible so as to lessen the likelihood of damage through mechanical shock or jarring. Also, in this connection, additional benefit from the referred to flexibility is gained inasmuch as said flexibility permits a disposition of the flexible portion so that it is less vulnerable to heat radiation.

A still further object which stems from the preceding object, is to provide a thermostat, the electrical contacts of which can be disposed in spaced relation with the soleplate or other electrically heated member to avoid unnecessary heating of said contacts.

Other objectswill be in part obvious and in part pointed out more in detail hereinafter.

The invention'accordingly consists in the features of construction, combination of elements and arrangement of parts which will be exemplified in the construction hereafter set forth and the scope of the application of which will be indicated in the appended claims.

In the drawing:

Figure 1 is a perspective view of an electrical flatiron showing the salient features of the invention;

Patented June 25, 1957 ice Figure 2 is a longitudinal view in section taken in the direction of line 2-2 of Figure 1.

Figure 3 is a perspective detail showing one part of the thermostat arrangement; and

Figure 4 is a view corresponding to Figure 3 but showing a slightly modified version of the part pictured in Figure 3.

To simplify the drawing as much as possible details of the iron unessential to an understanding of the invention have been omitted, such as, for instance, the handle and casing. Accordingly, that portion of the iron appearing in the drawing comprises a soleplate 10 having embedded therein a conventional heating element 12, and from an inspection of Figure 1 it will be observed that the heating element 12 has exposed ends 14 and 16 which provide means for connection to a source of electric power.

Near the forward end of the iron is mounted by means of screws 18 an inverted U-shaped bracket 20, there being laterally extending flanges 22 which permit the fixed anchoring of the bracket to the upper side of the soleplate. The bracket 26 includes a bridging portion 22 having formed thereon an upstanding tubular boss 24, the boss being internally threaded at 26. Threadedly received in the boss 24 is an adjusting sleeve 23 having at its upper end diametrically disposed slots for the accommodation of a manipulating knob (undisclosed). Within the bore of the sleeve 23 is threadedly received a calibration screw 32, the screw 32 having disposed at its upper end a slot 34 by means of which the screw may be rotated in initially setting the range of the thermostat, the details of which will be more fully described hereinafter. Fixedly circumscribing the sleeve 28 is a radially extending ear 36 which is arcuately moved when the sleeve 28 is rotated. The angular sweep of the car 36 is limited in opposite rotative directions by reason of a post 38 upstanding from the bridging portion 22.

The portion 22 is apertured at 40 for the reception of a tubular rivet 42. Beneath the bridging portion is an insulating washer 44 and subjacent this washer is a first switch blade or arm 4-6 having a contact 43 at its free end and a terminal portion 56 at its fixed end. Under the switch blade 46 is a second insulating washer 52 which serves to insulate the blade 46 from a second contact blade or arm 54. As is the case with the blade 46, the second blade carries at its free end a contact 56 cooperable with the previously mentioned contact 48 and at its fixed end there is provided a terminal 58. Enlarged, staked ends 59 on the rivet 42-2 assure that the stacked blades 45 and 54 are retained in proper juxtaposition.

As will be seen in Figure 2, the terminal St has electrical connection with the end 16 of the electric heating element 12 by way of an insulated conductor member 60. The other terminal 58 has a similar conductor member 62 connected thereto, this conductor member being shown only fragmentarily, as it will be appreciated that the other end of the conductor member 62 leads to the electric cord (not shown) which provides power to the heating element 12, the end 14 also leading to said cord.

By means of rivets 64 and an apertured anchoring plate 66, the upper end of a switch-operating member 68 is secured to the underside of the switch blade 54, the locus of se-curement being intermediate the free and fixed ends of this blade. The lower end of the operating member 68 is secured directly to the upper surface of the soleplate 10 by reason of a screw 70 and an anchoring plate 72 formed with an aperture 73. The purpose of the switchoperating member 68 is to actuate the switch contacts 48 and 56 into open position, these contacts being normally biased to closed position by virtue of the inherent resiliency of the switch blades 46 and 54 together with the 3 downward force provided by the screw 32. As will presently be made clearer, heating of the soleplate 10 will place the member under increased tension to produce separation or opening of the contacts.

To achieve an effective functioning of the thermostatic arrangement which includes the soleplate 10 and the member 68 it is exceedingly important that the member 68 have a very low coefiicient of expansion so that when the soleplate 10 expands, there will be an appreciable difference in total expansion between the soleplate 10 and said member 68. With this in mind, the invention enyisages the utilization of a stranded glass or ceramic material which will have a much smaller coefficient of expansion than the soleplate 10. At this point it might be mentioned that the two most common materials of which the soleplate is customarily made are aluminum and cast iron. Aluminum has a coefiicient of expansion of 24.0 l per C. and cast iron has a coefficient of 10.6)(' per C. In carrying out the objects of the invention it is contemplated that the member 68 be of ceramic material as liereinbefore indicated, and in this connection it has been found that either fused quartz or borosilicate glass be employed as the member 68. These mentioned materials have exceptionally low coefficients of expansion, the fused quartz being in the order of .0.25 10 per C. and the borosilicate glass being approximately 3.24 l0' per C. Thus even where the soleplate is of cast iron and the member 68 of borosilicate glass the ratio of coefficients of expansion of these two materials is less than one-third.

As best viewed in Figure 3 it can be discerned that the member or strip 63 may be woven or braided from drawn threads or strands of the aforenoted ceramic materials. These threads may best be described as being of the fibre-glass variety. This-type of construction permits ready handling of the strip 68 without need for undue caution against breakage thereof during the assembly procedure and the flexibility thereof assures continued durability.

Another recommended form that the low coefficient of expansion member may take is shown in Figure 4 and in this figure the member corresponding to the member 68 has been designated by the numeral 767 The member 76 consists of a pair of parallel individual strands or threads of either quartz or borosilicate glass, the ends thereof being retained in fixed relation with each other by reason of a pair of flattened sleeves 78 and 80. The sleeve 78 has an aperture passing therethrough labeled 82 and serves to accommodate the screw 70. The other sleeve 80 contains apertures 84 and accommodates the rivets 64.

Not only do fused quartz and borosilicate glass possess low coefficients of expansion but these materials have an added advantage of having low heat transfer rates. This last characteristic enables the lower end of either the member 68 or 76 to be anchored directly to the top side of the soleplate 10 and when so anchored, there is little tendency for heat to flow upwardly along either of these two members. Also, the inclination of the members 68 and 76 as suggested in Figure 1 permits these members to operate at a cooler temperature than they would if they were in close proximity throughout their length with the soleplate 10, for the major portion of each is then in spaced relation with the heated member 10 with the consequence that less heat will be radiated to the members 68 or 76. The inclination additionally permits the switch contacts 48 and 56 as well as their switch blades 46 and 54 to be mounted at an elevation above the soleplate, which elevation will allow the contacts to operate at a cooler temperature than they would if they were closely spaced with respect to the soleplate.

The functioning of an electrically heated iron, incorporating thereinto the thermostat function which is the subject matter of the instant invention, is believed readily apparent from the preceding description. Once the bracket fit) 20 has been fixedly positioned upon the soleplate 10 and the screw threaded into place, adjacent the heel or opposite end of the soleplate, the screw 32 is set so as to bring the switch blade 46 into proper initial position relative to the blade 54, thereby determining the operating temperature range. Subsequent adjustment of the blade 46 relative to the other blade 54 for operation within said range can be made by the ultimate user of the iron merely by turning the adjusting sleeve 28 to raise or lower the screw 32 threadedly contained therein.

After having set the control sleeve 28 for the desired ironing temperature, the heating element 12 via the usual cord (not shown) will be energized to supply heat to the soleplate. The soleplate, upon heating, will expand, and the distance between the screw and the bracket 20 will increase. However, the member 68, owing to its low coefficient of expansion helped by the particular disposition of such element relative to the soleplate, will not expand as much as the soleplate. Thus there will be a differential change in lengths of the member 68 and the soleplate member 10, which differential will be instrumental in pulling or tensioning the switch blade 54 downwardly, the tubular rivet 48 serving as a fulcrum point. The downward bending of the blade 54 causes the contacts 48 and 56 to separate and the heating element 12 then is deenergized and the soleplate begins to cool somewhat. Sufiicient cooling of the soleplate will cause a concomitant contraction thereof and the difference in expansion between the elements 68 and 10 lessens so that the resilient blade 54 moves upwardly once again to close the contacts 48 and 56. In this way a cyclic energization of the heating element 12 is achieved and the soleplate will be retained at substantially the temperature for which the sleeve 28 has been adjusted. Of course the iron will function in identical manner if the double strand member 76 is substituted for the braided or woven member 68.

As many changes could be made in the above construction any many apparently widely different embodiments of the invention could be made without departing from the scope thereof, it is intended that all matter contained in the above description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the language used in the following claims is intended to cover all of the generic and specific features of the invention herein described and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

Iclairn:

1. In an electrically heated appliance, a metallic plate having a relatively large coefiicient of expansion, an electric heating element for heating the plate, a switch unit fixedly supported with respect to one portion of the plate and spaced therefrom, said switch unit including a resilient switch blade and a pair of cooperable contacts in circuit with said heating element, one of which contacts is mounted on said switch blade for movement relative to the other contact, and an elongated fused flexible ceramic switch-operating means having one end fixedly anchored to another portion of the plate and its other end fixedly anchored to said switch blade for moving said movable contact relative to said other one, said ceramic means having a relatively low coefficient of expansion and extending angularly from its anchored locus away from said plate to said switch unit, whereby heating of said plate to a preselected temperature will cause said plate to expand to an appreciably greater extent than said ceramic means to place said ceramic means under sufficient tension to open said contacts.

2. The structure in accordance with claim 1 in which said plate has a coefficient of expansion greater than 10 10 per C. and said ceramic means has a coefficient of expansion less than 3.5 X10" per C.

3. The structure in accordance with claim 2 in which said ceramic means comprises fused quartz.

4. The structure in accordance with claim 2 in which said ceramic means comprises borosilicate glass.

5. In an electrically heated appliance, a metallic plate having a coefficient of expansion in excess of 10x10- per C., an electric heating element for heating. the plate, a switch unit fixedly disposed near one end of the plate including a pair of cooperable contacts in circuit with said heating element and a resilient contact blade supporting one of said contacts and biasing said contacts toward closed position, and an elongated braided fused ceramic switch-operating means having a coefiicient of expansion less than 3.5 X10 per C., one end of said ceramic means being anchored to the plate near its other end and the other end of said switch-operating means being anchored to said resilient blade, whereby heating of said plate to a preselected temperature will cause said plate to expand to an appreciably greater extent than said ceramic means to place said ceramic means under sufficient tension to overcome said bias and open said contacts.

6. The structure in accordance with claim 5 in which said ceramic means comprises fused quartz.

7. The structure in accordance with claim 5 in which said ceramic means comprises borosilicate glass.

8. In an electrically heated appliance, a metallic plate having a ccefiicient of expansion in excess of 10 per C., an electric heating element for heating the plate, a switch unit fixedly disposed near one end of the plate and spaced therefrom including a pair of cooperable contacts in circuit with said heating element and a resilient contact blade supporting one of said contacts and biasing said contacts toward closed position, and an elongated fused ceramic switch-operating means having a coefficient of expansion less than 3.5 10- per C., said ceramic means including a pair of substantially parallel flexible strands with one end being anchored to the plate near its other end and the other end being anchored to said resilient blade, said flexible strands extending iangularly from their anchored locus away from said plate to said switch unit, whereby heating of said plate to a preselected ironing temperature will cause said plate to expand to an 5 appreciably greater extent than said ceramic means to place said ceramic means under suflicient tension to overcome said bias and open said contacts.

9. The structure in accordance with claim 8 in which said ceramic means comprises fused quartz.

10. The structure in accordance with claim 8 in which said ceramic means comprises borosilicate glass.

11. in an electrically heated appliance, a metallic plate having a coeflicient of expansion greater than 10x10- per (3., an electric heating element for heating the plate, a switch unit including an upstanding bracket fixedly anchored near one end of the plate, a pair of resilient contact blades supported at one end above the plate by the bracket in a vertically spaced relationship with each other land a pair of cooperable contacts carried by said blades, and an elongated fused ceramic switchoperating means having a coeflicient of expansion less than 3.5 l0"' per C., said ceramic means inclining upwardly with its lower end being attached directly to the plate near its other end and its upper end being attached to the underside of the lower resilient blade intermediate its ends, whereby heating of said plate to a preselected temperature will cause said plate to expand to an appreciably greater extent than said ceramic means to fulcrum said lower blade downwardly about its fixed end to open said contacts.

12. The structure in accordance with claim 11 in which the bracket additionally supports threaded means for engaging and flexing the upper resilient blade to: obtain said preselected temperature.

References 'Cited in the file of this patent UNITED STATES PATENTS 1,075,991 Ruud Oct. 14, 1913 1,444,567 Sperr Feb. 6, 1923 1,776,240 Wunsch Sept. 16, 1930 2,024,856 Graham Dec. 17, 1935 2,052,662 Roehl et a1. Sept. 1, 1936 2,154,042 Gough Apr. 11, 1939 2,516,502 Altman et a1. July 25, 1950 

